chore: enable all staticcheck rules

[mmorel-35]

Thank you for contributing to Velero!

Please add a summary of your change

Enable staticcheck rules and fixes issues

Does your change fix a particular issue?

Fixes #(issue)

Please indicate you've done the following:

• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file (make new-changelog) or comment /kind changelog-not-required on this PR.
• Updated the corresponding documentation in site/content/docs/main.

[codecov]

Codecov Report

Attention: Patch coverage is 63.88889% with 52 lines in your changes missing coverage. Please review.

Project coverage is 59.71%. Comparing base (d2c6b6b) to head (3b84606).

Files with missing lines	Patch %	Lines
pkg/controller/pod_volume_backup_controller.go	0.00%	8 Missing and 3 partials ⚠️
pkg/controller/pod_volume_restore_controller.go	0.00%	6 Missing ⚠️
pkg/restore/restore.go	68.42%	4 Missing and 2 partials ⚠️
pkg/backup/actions/csi/pvc_action.go	42.85%	2 Missing and 2 partials ⚠️
pkg/backup/backup.go	50.00%	4 Missing ⚠️
pkg/controller/backup_deletion_controller.go	50.00%	1 Missing and 2 partials ⚠️
pkg/cmd/util/output/backup_structured_describer.go	0.00%	2 Missing ⚠️
pkg/controller/restore_controller.go	33.33%	2 Missing ⚠️
pkg/restore/actions/csi/pvc_action.go	50.00%	2 Missing ⚠️
pkg/backup/item_collector.go	85.71%	1 Missing ⚠️
... and 11 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8992      +/-   ##
==========================================
+ Coverage   59.70%   59.71%   +0.01%     
==========================================
  Files         370      370              
  Lines       40326    40325       -1     
==========================================
+ Hits        24075    24080       +5     
- Misses      14770    14773       +3     
+ Partials     1481     1472       -9     

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[mmorel-35]

/kind changelog-not-required

[kaovilai]

✅ LGTM - Excellent code quality improvements

This PR successfully enables all remaining staticcheck rules and fixes the resulting issues across 45 files. All changes are purely linter-driven improvements with no logical modifications:

Key improvements:

• Removes redundant field accesses and method calls
• Simplifies boolean logic patterns
• Eliminates unnecessary struct traversals
• Improves overall code readability

Impact: ✅ No functional changes, pure code quality enhancement
Risk: ✅ Very low - only stylistic improvements
Coverage: ✅ Comprehensive across the codebase

Great work on cleaning up technical debt and improving static analysis coverage!

Approved 👍